<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        var str='';
        var step='!';
        var arr=['yellow','white','black','red'];
        for( var i =0;i<arr.length;i++){
            str+=arr[i]+step;
        }
        alert(str);
    </script>
</head>
<body>
    
</body>
</html>